Muzzle loading rifles have an essentially closed breech at the rear of the barrel, so that powder and bullets must be loaded at the muzzle or forward end of the barrel. A typical muzzle loading rifle has a barrel with a breech plug attached to occupy an enlarged internally threaded rear bore portion of the barrel at the breech end. In some rifles, the breech plug is permanently attached. In others, the breech plug is removable to facilitate pass-through cleaning of the bore.
A typical removable breech plug employs a finely threaded elongated body that screws into the rear of the barrel, with 10-15 turns to secure it in place. The barrel's rear end is internally threaded to receive the plug, which removes for cleaning (not for normal loading operations.) The cleaning process involves the passing of a rod with a brush at the end through the entire length of the barrel. The brush, wetted with a liquid cleaning agent, dissolves and dislodges fouling, and it is dragged out of an end of the barrel. The fouled brush may pass over the internal threads at the breech, allowing the threads to become fouled. This is a concern because the barrel threads are cut to a tight tolerance for a close fit with the plug threads, and minor fouling can make the plug difficult to reinstall or remove after reinstallation.
In addition, breech plugs are generally larger in diameter than the bore of the barrel. This means that the wall thickness surrounding the plug is thinner than it is just forward of the plug in the chamber. In at least some instances, this wall diameter at the plug may be a strength limitation, requiring a larger barrel diameter than otherwise would be required, increasing manufacturing cost and/or weight.
The barrel must be designed to provide an adequate safety margin to retain the breech plug even in overpressure circumstances in the chamber. The barrel must have adequate thickness to resist excessive expansion in such extreme circumstances, to ensure that the barrel's internal threads do not fail to retain the plug.
Further, the length of a breech plug must be greater than an adequate threshold to provide strength to retain the pressure in the chamber. This length extends the length of the barrel without extending the length from the breech face to the muzzle. The added barrel length increases the weight and cost without the performance advantages of a lengthened barrel.
The elongated breech plug is a solid steel mass with only a small central bore to provide a fire passage between a primer and the chamber. The plug itself has appreciable mass to fill the required length and diameter, with weight reducing measures being generally impractical, even though lightness is generally desired in many rifles.
The present invention overcomes the limitations of the prior art by providing a muzzle loading firearm having an elongated barrel defining an elongated bore, with a muzzle end and a breech end. A breech cap is removably connected the breech end of the barrel to enclose a chamber at the rear of the bore. A portion of the breech cap may be external to the barrel, which may be externally threaded. The breech cap may be entirely clear of the breech bore, and the bore may have a consistent profile from end to end. The barrel threads may be standard, multistart or interrupted. The breech cap may overlay the face of the rear end of the barrel.